Semiconductor devices and methods of manufacture

ABSTRACT

A semiconductor device and method of manufacturing using carbon nanotubes are provided. In embodiments a stack of nanotubes are formed and then a non-destructive removal process is utilized to reduce the thickness of the stack of nanotubes. A device such as a transistor may then be formed from the reduced stack of nanotubes.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Application No.63/025,341, filed on May 15, 2020, which application is herebyincorporated herein by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as, for example, personal computers, cell phones, digital cameras,and other electronic equipment. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductor layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. As featuresize continues to shrink in semiconductor manufacturing process, morechallenges arise that need to be addressed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A-1B illustrate a filtering of a carbon nanotube solution, inaccordance with some embodiments.

FIGS. 2A-2B illustrate a placement of a stack of nanotubes onto asubstrate, in accordance with some embodiments.

FIGS. 3A-3B illustrates a thinning of the stack of nanotubes a firsttime, in accordance with some embodiments.

FIGS. 4A-4B illustrate a deposition of a supporting layer, in accordancewith some embodiments.

FIGS. 5A-5B illustrate a thinning of the stack of nanotubes a secondtime, in accordance with some embodiments.

FIGS. 6A-6B illustrate a removal of spacers from around the nanotubes,in accordance with some embodiments.

FIGS. 7A-7D illustrate a formation of a transistor, in accordance withsome embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments will now be described with respect to particular embodimentswhich utilize a vacuum system and filter in order to deposit and align astack of carbon nanotubes. Once the stack of carbon nanotubes is formed,a controlled reduction process can be utilized to make one or morelayers of carbon nanotubes, which are then used to form semiconductordevices. However, the embodiments presented herein are intended to beillustrative and are not intended to be limiting, as the ideas can beutilized in a wide variety of embodiments, such as various front end ofline (FEOL) processes and back end of line (BEOL) processes.

With respect now to FIGS. 1A-1B, there is illustrated a system 100 todeposit and align carbon nanotubes 101 (not seen in FIG. 1A butillustrated and described below with respect to FIG. 1B). In anembodiment the system 100 comprises a vacuum chamber 103 connected to afilter 105 through a connecting tube 107. In an embodiment the vacuumchamber 103 may be a chamber with both a first inlet 109 as well as afirst outlet 111. In an embodiment the vacuum chamber 103 may be sizedand shaped in order to enhance the ability of the vacuum chamber 103 tohelp carbon nanotubes 101 deposit and align within the system 100. Insome embodiments the vacuum chamber 103 may be shaped as an Erlenmeyerflask, although any suitable shape, such as a cylindrical shape, ahollow square tube, an octagonal shape, or the like, may also beutilized. Furthermore, the vacuum chamber 103 may be surrounded by ahousing 113 made of material that is inert to the various processmaterials. As such, while the housing 113 may be any suitable materialthat can withstand the chemistries and pressures involved in thefiltering process, in an embodiment the housing 113 may be glass, steel,stainless steel, nickel, aluminum, alloys of these, combinations ofthese, and like. However, any suitable materials may be utilized for thehousing 113 of the vacuum chamber 103.

A vacuum pump 115 may be connected to the first outlet 111. In anembodiment the vacuum pump 115 is utilized to help create the desiredvacuum within the vacuum chamber 103, which pressure differential canthen be utilized to help filter the carbon nanotubes 101 from a solutionand deposit the carbon nanotubes 101 onto the filter 105 by reducing andcontrolling the pressure within the vacuum chamber 103. However, anysuitable method of reducing the pressure in the vacuum chamber 103 maybe utilized.

The connecting tube 107 extends through a gasket and into the firstinlet 109 of the vacuum chamber 103 and connects the vacuum chamber 103to the filter 105. In an embodiment the connecting tube 107 works toconnect the vacuum chamber 103 to the filter 105, which allows thepressure differential to be applied between the vacuum chamber 103 andone side of the filter 105. In an embodiment the connecting tube 107 maybe any suitable material that can withstand the pressures andchemistries involved, and in some embodiments may be a material such asglass, steel, stainless steel, nickel, aluminum, alloys of these,combinations of these, and like. However, any suitable material may beutilized.

With reference now to the filter 105, FIG. 1A illustrates an exteriorview of the filter 105 and the location of the filter 105 within thesystem 100, while FIG. 1B illustrates an interior view of the filter105. As illustrated in FIG. 1B, in some embodiments the filter 105comprises a filter membrane 117 (not seen in FIG. 1A but seen in FIG.1B) that is utilized to filter the carbon nanotubes 101 from a carbonnanotube solution 123 as the carbon nanotube solution 123 is pulledthrough the filter membrane 117 by the pressure differential from thevacuum chamber 103. In an embodiment the filter membrane 117 may be amaterial such as polycarbonate, polytetrafluoroethene, or polyvinylidenefluoride, with a pore diameter that is smaller than the carbon nanotubes101 (in order to filter the carbon nanotubes 101), such as being betweenabout 0.01 μm and about 10 μm. However, any suitable material and anysuitable pore diameter may be utilized.

Additionally, while the pore size described above is sufficient tosimply remove the carbon nanotubes 101 from the carbon nanotube solution123, the use of a simple filter by itself may not be sufficient to alignthe carbon nanotubes 101 during the filtering process. As such, in someembodiments the filter membrane 117 is utilized to also generate anelectrostatic field (represented in FIG. 1B by the circled negativesigns labeled 119) that can be utilized to align the carbon nanotubes101 as the carbon nanotubes 101 enter into the electrostatic field 119during the filtering process. In some embodiments the electrostaticfield 119 may be passively generated while in other embodiments theelectrostatic field 119 may be actively generated during the filteringprocess.

Looking first at embodiments in which the electrostatic field 119 isgenerated passively, the filter membrane 117 may be used to create theelectrostatic field 119 by coating the filter membrane 117 with acoating material (not separately illustrated in FIG. 1B for clarity)that will passively create the desired electrostatic field 119. In anembodiment the coating material may comprise a hydrophilic material suchas poly(vinylpyrrolidone) (PVP), hexamethyldisilazane (HMDS), aluminumoxide (Al₂O₃), combinations of these, or the like. However, any suitablematerial may be utilized.

In embodiments in which poly(vinylpyrrolidone) is utilized as thecoating material, the poly(vinylpyrrolidone) will passively generate thedesired electrostatic field 119. In such embodiments, the electrostaticfield 119 may have a voltage of between about 0 V and about 10 V at adistance of between about 0 nm and about 10 nm. However, any suitableelectrostatic field 119 may be generated using passive generation, andall such methods of generating the electrostatic field may be utilized.

In another embodiment the electrostatic field 119 can be activelygenerated either prior to or during the filtering process by capturingnegative charges. In such an embodiment, instead of permanently coatingthe filter membrane 117 with a single material, the filter membrane 117is actively charged prior to the filtering process with a surfactant.For example, in some embodiments the surfactant may be a negativelycharged material such as sodium dodecyl sulfate (SDS), sodiumdodecylbenzenesulfonate (SDBS), sodium deoxycholate (DOC), combinationsof these, or the like. However, any suitable surfactants may beutilized.

In an embodiment the surfactant may be introduced to the filter membrane117 prior to introduction of the carbon nanotube solution 123. In anembodiment the surfactant may be introduced to the filter membrane 117by flowing the surfactant over and/or through the filter membrane 117 sothat at least a portion of the negative charge from the surfactant iscaptured on the filter membrane 117 and remains at least partially inplace during a subsequent filtering process.

In another embodiment the surfactant may be included as part of thecarbon nanotube solution 123. In such an embodiment the surfactant maybe included in the carbon nanotube solution 123 instead of flowing thesurfactant over the filter membrane 117 prior to introduction of thecarbon nanotube solution 123. In other embodiments the surfactant may beflowed over the filter membrane 117 before the filtering process and isalso introduced again within the carbon nanotube solution 123. Anysuitable combination of processes to introduce the surfactant to thefilter membrane 117 may be utilized, and all such processes are fullyintended to be included within the scope of the embodiments.

In embodiments in which the electrostatic field 119 is generated using asurfactant in an active generation process, the surfactant will activelygenerate the desired electrostatic field 119 in each filtering process.In such embodiments, the electrostatic field 119 may have a voltage ofbetween about 0 V and about 10 V at a distance of between about 0 nm andabout 10 nm. However, any suitable electrostatic field 119 may begenerated using active generation, and all such methods of generatingthe electrostatic field may be utilized.

Returning now to FIG. 1A, FIG. 1A additionally illustrates a solutioncontainer 121 connected to one side of the filter 105 that is oppositethe vacuum chamber 103. In an embodiment the solution container 121 maybe used to store and/or supply a carbon nanotube solution 123 (see FIG.1B) to the filter 105. In one embodiment the solution container 121 maybe a container of a material that can withstand the pressure andchemistries involved in the filtration process, and in some embodimentsmay be a material such as glass, steel, stainless steel, nickel,aluminum, alloys of these, combinations of these, and the like. However,any suitable material may be utilized.

In another embodiment the solution container 121 may be an entrance forthe carbon nanotube solution 123 to enter the filter 105 while thecarbon nanotube solution 123 may be stored and/or even createdseparately from the filter 105. For example, in some embodiments thecarbon nanotube solution 123 may be mixed and/or stored prior to theintroduction of the carbon nanotube solution 123 to the filter 105, andthe solution container 121, instead of being a stand-alone system thatis attached and removed from the system 100, is a supply system whichprovides a steady supply of the carbon nanotube solution 123 during thefiltering process.

The carbon nanotube solution 123 comprises the carbon nanotubes 101dispersed within a solvent 125. In an embodiment the carbon nanotubes101 may be single-walled carbon nanotubes formed using any suitablemethod, such as a carbon arc discharge method (with subsequentpurification), a laser vaporization method, a catalyzed chemical vapordeposition, ball milling and subsequent annealing, diffusion flamesyntheses, electrolysis, heat treatment of a polymer, low-temperaturesolid pyrolysis, combinations of these, or the like. However, anysuitable method of manufacturing the carbon nanotubes 101 may beutilized, and all such methods are fully intended to be included withinthe scope of the embodiments.

Optionally, in some embodiments the carbon nanotubes 101 may besurrounded by spacers 129 which can provide a dual purpose of acting asa purification agent for the carbon nanotubes 101 as well as working tohelp disperse the carbon nanotubes 101 within the carbon nanotubesolution 123. Additionally, by controlling the thickness of the spacers129 around each of the carbon nanotubes 101, the spacing of the carbonnanotubes 101 once the carbon nanotubes 101 have been aligned adjacentto each other can also be controlled.

In an embodiment the spacers 129 can be a material which can be placedand removed from the carbon nanotubes as desired, while also notdetrimentally interfering with the manufacturing processes betweenplacement and removal. For example, in particular embodiments thespacers 129 may be a material such as a surfactant (e.g., sodium dodecylsulfate, sodium dodecylbenzenesulfonate, sodium deoxycholate, etc.), apolymer (e.g.,poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt-co-(6,6′-{2,2′-bipyridine}),isoindigo-based poly (9, 9-dioctylfluorene),poly[9-(1-octylonoyl)-9H-carbazole-2,7-diyl, etc.), a dielectricmaterial (e.g., HfO₂/SiO₂/Al₂O, etc.) or even other nanotubes (e.g., aboron nitride nanotube, a MoS₂ nanotube, etc.). However, any suitablematerial or combination of materials may be utilized to surround andcoat the carbon nanotubes 101 during the filtering process.

The spacers 129 may be placed around the carbon nanotubes 101 using anysuitable process. For example, processes such as chemical vapordeposition, atomic layer deposition, surfactant wrapping, polymerwrapping, combinations of these, or the like, may be utilized to placethe spacers 129 around the individual carbon nanotubes 101.Additionally, in embodiments in which the spacers 129 are utilized tocontrol the spacing between adjacent carbon nanotubes 101 once thecarbon nanotubes 101 have settled adjacent to each other, the spacers129 may have a thickness from between about 0 Å to about 10 nm. However,any suitable method of placement and any suitable thickness may beutilized.

In an embodiment the carbon nanotube solution 123 is formed by placingthe carbon nanotubes 101 (with or without the spacers 129) into asolvent 125. In an embodiment the solvent 125 may be utilized to containthe carbon nanotubes 101 during transport and also to provide a suitablemedium for the carbon nanotubes 101 to settle in the desired orderorientation (described further below) during the filtering process. Insome embodiments the solvent 125 may be a solvent such as water (H₂O),toluene, trichloroethane, tetrahydrofuran, or chloroform. However, anysuitable material for the solvent 125 may be utilized.

In an embodiment the carbon nanotubes 101 may have a concentrationwithin the solvent 125 that is high enough to allow for an efficientsettling of the carbon nanotubes 101 while also not so high that thesheer number of carbon nanotubes 101 interferes with the settlingprocess. As such, the carbon nanotubes 101 may have a concentrationwithin the carbon nanotube solution 123 of between about 0.001 mg/ml andabout 1 mg/ml. However, any suitable concentration may be utilized.

Additionally, while the carbon nanotube solution 123 is described ascomprising the solvent 125 and the carbon nanotubes 101, thisdescription is intended to be illustrative and is not intended to belimiting. In particular, the carbon nanotube solution 123 may compriseany other suitable or desirable additives, such as the surfactant thatis utilized for an active generation of the desired electrostatic field119. All such additives are fully intended to be included within thescope of the embodiments.

To initiate the filtering process, the carbon nanotube solution 123 isplaced within the solution container 121 and the solution container 121is connected to the filter 105 so that the carbon nanotube solution 123is able to flow to the filter membrane 117. Additionally, a vacuum iscreated in the vacuum chamber 103 using the vacuum pump 115 as a drivingforce to pull the carbon nanotube solution 123 through the filtermembrane 117. In an embodiment, the vacuum pump 115 connected to thefirst outlet 111 can be utilized to reduce the pressure in the vacuumchamber 103 to between about 1 mtorr and about 760 torr. However, anysuitable pressure may be utilized.

With the vacuum in place within the vacuum chamber 103, a pressuredifferential is created between a first side of the filter membrane 117facing the vacuum chamber 103 and a second side of the filter membrane117 facing the carbon nanotube solution 123. With the pressuredifferential applied, the carbon nanotube solution 123 is pulled throughthe filter membrane 117, filtering the carbon nanotubes 101 from thesolvent 125 as the solvent 125 passes through the filter membrane 117while the filter membrane 117 captures the carbon nanotubes 101 that aretoo large to pass through the filter membrane 117.

Additionally, with the presence of the electrostatic field 119 on thefilter membrane 117 (generated either passively or actively), acombination of the electrostatic field 119 and Van der Waals attractionwill also work to align the carbon nanotubes 101 as the carbon nanotubes101 settle onto the filter membrane 117, so that the carbon nanotubes101 settle parallel and aligned to each other. In particular, in anembodiment in which the carbon nanotubes 101 have a negative charge(e.g., from the negatively charged surfactants wrapped around the carbonnanotubes 101 as the spacers 129) and the electrostatic field 119 alsohas a negative charge, the electrostatic field 119 will work to forcethe carbon nanotubes 101 to align parallel with each other as the carbonnanotubes 101 are filtered by the filter membrane 117.

As the filtering process continues, the carbon nanotubes 101 within thecarbon nanotube solution 123 are deposited as a first layer 131 of thecarbon nanotubes 101, wherein within the first layer 131 the carbonnanotubes 101 are aligned next to each other. Additionally, once thefirst layer 131 of the carbon nanotubes 101 are deposited, a secondlayer 201 of the carbon nanotubes 101, a third layer 203 of the carbonnanotubes 101, a fourth layer 205 of the carbon nanotubes 101, a fifthlayer 207 of the carbon nanotubes 101, and a sixth layer 209 of thecarbon nanotubes 101 are deposited in order to form a stack 211 (notillustrated in FIG. 1B but illustrated and described further below withrespect to FIG. 2A) of carbon nanotubes 101. Any suitable number oflayers of the carbon nanotubes 101 may be deposited during the filteringprocess.

FIGS. 2A-2B illustrate that, once the stack 211 of carbon nanotubes 101has been deposited on the filter membrane 117, the stack 211 of carbonnanotubes 101 may be transferred to a first dielectric layer 215 locatedover a first substrate 217, with FIG. 2A illustrating a cross sectionalview of the top down view of FIG. 2B through line A-A′. In an embodimentthe first substrate 217 may be a support material such as a siliconmaterial (e.g., a silicon wafer), a germanium material, a silicongermanium material, a gallium arsenide material, although othersubstrates, such as semiconductor-on-insulator (SOI), strained SOI,silicon germanium on insulator, glass substrate, combinations of these,or the like. However, any suitable material may be used for the firstsubstrate 217.

The first dielectric layer 215 is located over the first substrate 217and is utilized to isolate devices subsequently formed on the firstsubstrate 217. In an embodiment the first dielectric layer 215 is adielectric material such as silicon oxide, aluminum oxide, combinationsof these, or the like deposited onto the first substrate 217 using adeposition process such as chemical vapor deposition, sputtering, atomiclayer deposition, combinations of these, or the like. However, anysuitable material and any suitable deposition process may be utilized.

Additionally, while FIG. 2A illustrates the first dielectric layer 215as being directly on and in physical contact with the first substrate217, this is intended to be illustrative and is not intended to belimiting. Rather, other dielectric materials and other substratematerials (e.g., silicon, germanium, gallium arsenide, combinations ofthese, or the like) may also be present between the first dielectriclayer 215 and the first substrate 217. All such combinations of layersmay be used, and all are fully intended to be included within the scopeof the embodiments.

Once the first dielectric layer 215 is located over the first substrate217, the stack 211 of carbon nanotubes 101 are transferred from thefilter membrane 117 to the first dielectric layer 215. In an embodimentthe transfer may be performed by initially removing the filter membrane117 from the system 100 and then applying a transfer layer (notseparately illustrated) to the stack 211 of carbon nanotubes 101. In anembodiment the transfer layer may be a material that may be used to holdand protect the stack 211 of carbon nanotubes 101 while also allowingfor an easy removal of the transfer layer once the stack 211 of carbonnanotubes 101 has been transferred. For example, the transfer layer maybe polycarbonate (PC), polymethyl-methacrylate (PMMA), although anyother suitable material, such as methyacrylic resin or Novolac resin, orthe like, may alternatively be utilized.

In an embodiment in which the transfer layer is PMMA, the transfer layermay be placed on the stack 211 of carbon nanotubes 101 using, e.g., aspin-coating process, although any other suitable deposition process mayalso be utilized. Once in place, the PMMA may be cured and solidified.This solidified PMMA both protects the stack 211 of carbon nanotubes 191and also allows for the movement and control of the stack 211 of carbonnanotubes 191 through the transfer layer.

Once the transfer layer has been put into place over the stack 211 ofcarbon nanotubes 101, the transfer layer may be utilized to place thestack 211 of carbon nanotubes 101 over the first substrate 217 and incontact with the first dielectric layer 215. The placement of the stack211 of carbon nanotubes 101 may be performed by controlling the transferlayer (with the stack 211 of carbon nanotubes 101 attached) and usingthe transfer layer to place the stack 211 of carbon nanotubes 101.

Additionally, in certain embodiments the stack 211 of carbon nanotubes101 may have a greater alignment along one surface of the stack 211 thanalong another surface of the stack 211. In such embodiments, the stack211 of carbon nanotubes 101 may be placed so that the surface with thegreater alignment is facing or in physical contact with the firstsubstrate 217. However, any suitable placement may be utilized.

Once the stack 211 of carbon nanotubes 101 has been placed on the firstdielectric layer 215, the transfer layer may be removed. In anembodiment the transfer layer may be removed using a stripping oretching process to remove the material of the transfer layer from thestack 211 of carbon nanotubes 101. As such, while the materials utilizedto remove the transfer layer may be at least in part dependent upon thematerial chosen for the transfer layer, in an embodiment in which thetransfer layer is PMMA, the transfer layer may be removed by applyingacetone to the PMMA, which dissolves the PMMA.

However, as one of ordinary skill in the art will recognize, the use ofPMMA for the transfer layer, and the use of the transfer layer ingeneral, is not intended to limit the embodiments. Rather, any suitablemethod of transferring the stack 211 of carbon nanotubes 101 andintegrating the stack 211 of carbon nanotubes 101 into a manufacturingprocess flow may be utilized. Any other suitable method for transferringthe stack 211 of carbon nanotubes 101 are fully intended to be includedwithin the scope of the embodiments.

Once the stack 211 of carbon nanotubes 101 has been transferred, thestack 211 of carbon nanotubes 101 may have between about 30 layers ofcarbon nanotubes 101 and about 60 layers of carbon nanotubes. As such,the stack 211 of carbon nanotubes 101 may have a thickness of betweenabout 50 nm and about 100 nm. However, any suitable number of carbonnanotubes 101 and any suitable thickness may be utilized.

Additionally, by using the solution based filtering method as describedabove, a high density, extremely pure layer of the carbon nanotubes 101may be obtained. For example, the carbon nanotubes may have a purity ofgreater than about 99.99%. Additionally, within each layer of the carbonnanotubes 101, there may be a density of about 500 carbon nanotubes permicron. However, any suitable purity and any suitable density may beutilized.

FIGS. 3A-3B illustrate that, once the stack 211 of carbon nanotubes 101has been transferred to the first dielectric layer 215, a thickness ofthe stack 211 of carbon nanotubes 101 may be reduced, with FIG. 3Aillustrating a cross sectional view of the top down view of FIG. 3Bthrough line A-A′. In an embodiment the reduction may be performed usinga destructive thinning process (represented in FIG. 3A by the arrowslabeled 301). For example, in some embodiments the destructive thinningprocess 301 may be performed using a process such as reactive ion dryetching, sonication thinning, dissolution thinning, chemicalintercalation thinning, mechanical grinding, chemical mechanicalpolishing, chemical polishing, combinations of these, or the like.However, any suitable thinning process may be utilized.

In an embodiment the stack 211 of carbon nanotubes 101 may be thinned sothat only a desired number of carbon nanotubes (e.g., the first layer131 of carbon nanotubes 101 and the second layer 201 of carbon nanotubes101) remain within a reduced stack 303 of the carbon nanotubes 101. Inan embodiment the reduced stack 303 of carbon nanotubes 101 may havebetween about 3 layers of carbon nanotubes 101 and about 6 layers ofcarbon nanotubes. As such, the reduced stack 303 of carbon nanotubes 101may have a thickness of between about 5 nm and about 10 nm. However, anysuitable number of carbon nanotubes 101 and any suitable thickness maybe utilized.

However, the destructive thinning processes 301 as described above arenot perfect. As such, while many of the carbon nanotubes 101 that aredesired to be removed are actually removed, the use of the destructivethinning processes 301 will also damage, but may not remove, at leastsome of the carbon nanotubes 101 that had been present in the layersthat were desired to be removed (e.g., the third layer 203 of the carbonnanotubes 101, the fourth layer 205 of the carbon nanotubes 101, thefifth layer 207 of the carbon nanotubes 101, and the sixth layer 209 ofthe carbon nanotubes 101), thereby forming damaged carbon nanotubes 305.

FIGS. 4A-4B illustrate that, once the stack 211 of carbon nanotubes 101has been reduced to the reduced stack 303 of the carbon nanotubes 101, asupporting layer 401 is deposited over the reduced stack 303 of thecarbon nanotubes 101, with FIG. 4A illustrating a cross sectional viewof the top down view of FIG. 4B through line A-A′. In an embodiment thesupporting layer 401 works as an adhesion layer for a subsequentnon-destructive thinning process (not illustrated in FIGS. 4A-4B butillustrated and discussed further below with respect to FIGS. 5A-5B). Assuch, in some embodiments the material of the supporting layer 401 maybe a metal such as nickel, molybdenum, tungsten, platinum, bismuth,combinations of these, or the like. In such an embodiment the materialof the supporting layer 401 may be deposited using an evaporationdeposition process, a chemical vapor deposition process, a sputteringprocess, an atomic layer deposition process, combinations of these, orthe like. Any suitable deposition process may be utilized.

In other embodiments the supporting layer 401 may be an organic materialsuch as polymethyl methacrylate (PMMA), polyvinyl acetate (PVA),polyvinylpyrrolidone (PVP), polypropylene carbonate (PPC), otherpolyaromatic hydrocarbons (PAHs), phenyltrimethoxysilane (PTMS),polydimethylsiloxane (PDMS), rosin, combinations of these, or the like.In embodiments such as this, the material of the supporting layer 401may be deposited using a deposition method such as spin-coating or thelike. However, any suitable material and method of deposition may beutilized.

FIGS. 5A-5B illustrate that, once the supporting layer 401 has beendeposited, additional ones of the carbon nanotubes 101 (e.g., the secondlayer 201 of carbon nanotubes) are removed from the reduced stack 303 ofthe carbon nanotubes 101 to form an operational layer 503, with FIG. 5Aillustrating a cross sectional view of the top down view of FIG. 5Bthrough line A-A′. In an embodiment, and to avoid damage to underlyinglayers, the additional ones of the carbon nanotubes 101 are removedusing a non-destructive thinning process (represented in FIG. 5A by thearrows labeled 501).

In some embodiments the non-destructive thinning process 501 may beperformed by removing the supporting layer 401 using a process such asmechanical exfoliation. In a particular embodiment which uses mechanicalexfoliation, an adhesive material such as a Scotch-type tape may beapplied to the supporting layer 401. Once applied and adhered to thesupporting layer 401, a force may be applied to the adhesive material toremove the supporting layer 401.

However, in addition to simply removing the supporting layer 401 byitself, the removal of the supporting layer 401 will additionally removethe damaged carbon nanotubes 305 which are covered by the supportinglayer 401 as well as one or more layers of the carbon nanotubes 101(e.g., the second layer 201 of the carbon nanotubes 101 in FIG. 5A). Assuch, the non-destructive thinning process 501 can be utilized to removethe damaged carbon nanotubes 305 so that the damaged carbon nanotubes305 cannot interfere with subsequent processes. Additionally, thenon-destructive thinning process 501 can further be used to further thinthe reduced stack 303 of the carbon nanotubes 101 without generatingadditional damaged carbon nanotubes 101.

Additionally, while the mechanical exfoliation process described aboveis one such process which may be utilized to remove the supporting layer401 and reduce the thickness of the reduced stack 303, this descriptionis intended to be illustrative and is not intended to be limiting.Rather, any suitable non-destructive thinning process, such as using asacrificial metal layer for thinning by carbon diffusion during anneal,using a removal of the spacers 129 inserted into the structured carbonnanotube film (e.g., the stack 211) using either chemical methods or avacuum anneal, or thinning of the reduced stack 303 by sonication ormechanical releases, may also be utilized. Any such method ofnon-destructive thinning may be utilized and all such methods are fullyintended to be included within the scope of the embodiments.

Once the operational layer 503 of carbon nanotubes 101 has been formed,the operational layer 503 of carbon nanotubes 101 may have a singlelayer of carbon nanotubes 101. As such, the operational layer 503 ofcarbon nanotubes 101 may have a thickness of between about 1 nm andabout 1.5 nm. However, any suitable number of carbon nanotubes 101 andany suitable thickness may be utilized.

In the embodiment illustrated in FIGS. 3A-5B, the destructive thinningprocess 301 may be performed to reduce the stack 211 of carbon nanotubes101 to have only two of the layers of carbon nanotubes 101 while thenon-destructive thinning process 501 removes only a single layer of thecarbon nanotubes 101 to leave behind a single layer of the carbonnanotubes. This, however, is intended to be illustrative and is notintended to be limiting to the embodiments. Rather, any suitablecombinations or repetition of steps may be utilized to obtain theoperational layer 503 of the carbon nanotubes 101.

For example, in some embodiments the destructive thinning process 301may be omitted entirely or else be performed to remove only a minimalnumber of layers of the carbon nanotubes 101 (e.g., remove one or twolayers of the carbon nanotubes 101). In such an embodiment most or allof the thinning to obtain the operational layer 503 of the carbonnanotubes 101 is performed using the non-destructive thinning process501. Additionally, if one such non-destructive thinning process 501 isnot sufficient to thin the stack 211 of the carbon nanotubes 101, thenon-destructive thinning process 501 may be repeated one or more timesin order to remove successive layers of the carbon nanotubes 101 untilthe desired number of layers of carbon nanotubes 101 has been obtained.Any suitable number of iterations in any order may be used, and all suchcombinations are fully intended to be included within the scope of theembodiments.

FIGS. 6A-6B illustrate that, once the operational layer 503 of thecarbon nanotubes 101 has been formed, the spacers 129 may optionally beremoved from around the carbon nanotubes 101, with FIG. 6A illustratinga cross sectional view of the top down view of FIG. 6B through lineA-A′. In an embodiment in which the spacers 129 are a surfactant or apolymer, the spacers 129 may be removed using an annealing process,whereby a temperature of the material of the spacers 129 is increaseduntil either the material evaporates (if possible) or else suffers athermal decomposition, after which the material may be easily removed.

In another embodiment in which the material of the spacers 129 is adielectric material, the spacers 129 may be removed using an etchingprocess. In a particular embodiment the spacers 129 may be removed usinga wet etching process with an etchant that is selective to the materialof the spacers 129. However, any suitable etching or other removalprocess may be utilized.

By utilizing the spacers 129 during alignment and then removing thespacers 129, the pitch of the remaining carbon nanotubes 101 may beprecisely controlled by controlling the thickness of the spacers 129. Assuch, in some embodiments the carbon nanotubes 101 may have a pitch ofbetween about 0 nm and about 100 nm. However, any suitable pitch may beutilized.

FIGS. 7A-7B illustrate an isometric view (in FIG. 7A) and a top downview (in FIG. 7B) in which the operational layer 503 of the carbonnanotubes 101 are utilized to form a planar transistor 700. In addition,FIG. 7C illustrates a first cross-sectional view of the planartransistor 700 through line C-C′ and FIG. 7D illustrates a secondcross-sectional view of the planar transistor 700 through line D-D′. Inparticular, once the operational layer 503 of the carbon nanotubes 101has been formed, source/drain contacts 707 may be formed, gate spacers705 may be formed, a gate dielectric 701 may be formed, and a gateelectrode 703 may be formed. However, any suitable combination ofstructures may be utilized.

In an embodiment the source/drain contacts 707 may be formed on oppositesides of a channel region located within the carbon nanotubes 101 and incontact with the sidewalls of source/drain regions which are alsolocated within the carbon nanotubes 101 on opposite sides of the channelregion. In accordance with some embodiments, the formation of thesource/drain contacts 707 includes forming and patterning an etchingmask such as a photoresist (not separately illustrated in FIGS. 7A-7D)so that the regions in which the source/drain contacts 707 are to beformed are exposed, while other regions are covered by the etching mask.A conductive layer such as a metal layer (e.g., tungsten, cobalt,combinations of these, or the like) is then deposited as a blanketlayer. A lift-off process is then performed, with the etching mask beinglifted off, and the portions of the conductive layer on the etching maskalso being removed. As such, source/drain contacts 707 are left as shownin FIGS. 7A-7D.

Once the source/drain contacts 707 have been formed, the gate spacers705 may be formed in order to separate the source/drain contacts 707from the gate electrode 703. In an embodiment the gate spacers 705 maybe formed by conformally depositing an insulating material andsubsequently anisotropically etching the insulating material. Theinsulating material of the gate spacers 705 may be silicon oxide,silicon nitride, silicon oxynitride, silicon carbonitride, a combinationthereof, or the like. However, any suitable material and depositionprocess may be utilized.

Once the material for the gate spacers 705 has been formed, the gatedielectric 701 may be formed. In an embodiment the gate dielectric 701comprises one or more dielectric layers, such as one or more layers ofsilicon oxide, silicon nitride, metal oxide, metal silicate, or thelike. For example, in some embodiments, the gate dielectric 701 includesa high-k dielectric material, such as a metal oxide or a silicate ofhafnium, aluminum, zirconium, lanthanum, manganese, barium, titanium,lead, and combinations thereof. The gate dielectric 701 may include adielectric layer having a k value greater than about 7.0. The formationmethods of the gate dielectric 701 may include depositing a gatedielectric layer (not separately illustrated in FIGS. 7A-7D) through adeposition process such as Molecular-Beam Deposition (MBD), ALD, PECVD,and the like. However, any suitable materials and methods of manufacturemay be utilized to deposited the material for the gate dielectric 701.

Once the material for the gate dielectric 701 has been deposited, thematerial for the gate electrode 703 is deposited. The material for thegate electrode 703 may be formed by initially forming a gate electrodelayer (not separately illustrated in FIGS. 7A-7D). In an embodiment thegate electrode layer comprises a conductive material and may be selectedfrom a group comprising of polycrystalline-silicon (poly-Si),polycrystalline silicon-germanium (poly-SiGe), metallic nitrides,metallic silicides, metallic oxides, and metals. Examples of metallicnitrides include tungsten nitride, molybdenum nitride, titanium nitride,and tantalum nitride, or their combinations. Examples of metallicsilicide include tungsten silicide, titanium silicide, cobalt silicide,nickel silicide, platinum silicide, erbium silicide, or theircombinations. Examples of metallic oxides include ruthenium oxide,indium tin oxide, or their combinations. Examples of metals includetantalum, tungsten, titanium, aluminum, copper, molybdenum, nickel,platinum, etc.

In an embodiment the gate electrode layer may be deposited by chemicalvapor deposition (CVD), sputter deposition, or other techniques knownand used in the art for depositing conductive materials. The thicknessof the gate electrode layer may be in the range of about 200 angstromsto about 4,000 angstroms. The top surface of the gate electrode layerusually has a non-planar top surface, and may be planarized prior topatterning of the gate electrode layer or gate etch. Dopants may or maynot be introduced into the gate electrode layer at this point. Dopantsmay be introduced, for example, by molecular doping techniques thrucharge transfer.

Once the gate electrode layer has been formed, the gate electrode layer,the gate dielectric layer, and the gate spacers 705 may be planarized.In an embodiment the material of the gate electrode layer and thematerial of the gate dielectric layer are planarized to form the gateelectrode 703 and the gate dielectric 701 using, e.g., a chemicalmechanical polishing process. However, any suitable method ofplanarization may be utilized.

Once planarized, if desired, the source/drain contacts 707 may beexposed from any remaining overlying material (e.g., the material of thegate spacers 705). In some embodiments the source/drain contacts 707 maybe exposed using, for example, a photolithographic masking and etchingprocess, whereby a photoresist is deposited and patterned in order tooverly and protect portions of the gate spacers 705, the gate dielectric701, and the gate electrode 703, while exposing other portions. Onceprotected, an etching process, such as a reactive ion etching process,may be utilized in order to expose portions of the source/drain contacts707. However, any suitable process may be utilized to expose thesource/drain contacts 707 for further processing, such as formation ofan overlying metallization layer.

By utilizing the non-destructive thinning process 501 to perform thefinal thinning steps and obtain the operational layer 503, any damagedcarbon nanotubes 101 may be removed from the structure and will not bepresent to potentially interfere with subsequent manufacturingprocesses. Additionally, such a process allows for a greater degree ofcontrol over the thinning process, allowing for very precisedetermination of how many layers of carbon nanotubes 101 can be used.All of these benefits help to increase yield and make the process moreefficient by preventing defects that may otherwise occur and formsdevices with improved performance to achieve targets beyond the 2 nmnode.

In an embodiment, a method of manufacturing a semiconductor device, themethod includes: forming a stack of nanotubes, wherein individualnanotubes are aligned with adjacent nanotubes; depositing a supportinglayer over the stack of nanotubes; removing the supporting layer,wherein the removing the supporting layer further removes at least onelayer of nanotubes from the stack of nanotubes; and depositing a gateelectrode over a remaining portion of the stack of nanotubes. In anembodiment the method further includes, after the removing thesupporting layer, removing a spacer material from around at least onenanotube within the remaining portion of the stack of nanotubes. In anembodiment the forming the stack of nanotubes comprises filtering theindividual nanotubes through a filter membrane. In an embodiment thefilter membrane has a first electrostatic field during the filtering theindividual nanotubes. In an embodiment the individual nanotubes aresurrounded by a spacer material during the filtering the individualnanotubes, the spacer material having a second electrostatic field. Inan embodiment the stack of nanotubes has a nanotube density of about 500nanotubes per micrometer. In an embodiment the spacer material comprisesa surfactant.

In another embodiment, a method of manufacturing a semiconductor deviceincludes: filtering a carbon nanotube solution through a filtermembrane, the filter membrane having a electrostatic field, whereinduring the filtering a first layer of carbon nanotubes, a second layerof carbon nanotubes, and a third layer of carbon nanotubes are depositedon the filter membrane; transferring the first layer of carbonnanotubes, the second layer of carbon nanotubes, and the third layer ofcarbon nanotubes to a dielectric layer over a substrate; removing thethird layer of carbon nanotubes with a destructive removal process;removing the second layer of carbon nanotubes with a non-destructiveremoval process; and forming a gate electrode over the first layer ofcarbon nanotubes after the removing the second layer of carbonnanotubes. In an embodiment the destructive removal process comprises areactive ion etching process. In an embodiment the non-destructiveremoval process comprises a mechanical exfoliation process. In anembodiment the mechanical exfoliation process further comprisingdepositing a supporting layer over the second layer of carbon nanotubes,and wherein the mechanical exfoliation process removes both thesupporting layer and the second layer of carbon nanotubes. In anembodiment the mechanical exfoliation process further removes carbonnanotubes damaged during the destructive removal process. In anembodiment the method further includes removing a spacer material fromcarbon nanotubes within the first layer of carbon nanotubes. In anembodiment the first layer of carbon nanotubes has a density of about500 nanotubes per micrometers.

In yet another embodiment, a method of manufacturing a semiconductordevice includes: receiving a solution, the solution comprising carbonnanotubes; aligning the carbon nanotubes using a first electrostaticfield into a stack of aligned carbon nanotubes; placing the stack ofaligned carbon nanotubes onto a dielectric material; thinning the stackof aligned carbon nanotubes a first time with a first process; thinningthe stack of aligned carbon nanotubes a second time with a secondprocess different from the first process; and depositing a source/draincontact in electrical connection with the stack of aligned carbonnanotubes after the thinning the stack of aligned carbon nanotubes thesecond time. In an embodiment after the thinning the stack of alignedcarbon nanotubes the second time a thickness of the stack of alignedcarbon nanotubes is less than 2 nm. In an embodiment the first processis an etching process. In an embodiment the second process is anexfoliation process. In an embodiment the first electrostatic field isgenerated by a material located on a filter membrane. In an embodimentthe carbon nanotubes are surrounded by a spacer material during thealigning the carbon nanotubes, the spacer material generating a secondelectrostatic field.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method of manufacturing a semiconductor device,the method comprising: forming a stack of nanotubes, wherein individualnanotubes are aligned with adjacent nanotubes; depositing a supportinglayer over the stack of nanotubes; removing the supporting layer,wherein the removing the supporting layer further removes at least onelayer of nanotubes from the stack of nanotubes; and depositing a gateelectrode over a remaining portion of the stack of nanotubes.
 2. Themethod of claim 1, wherein the forming the stack of nanotubes comprisesfiltering the individual nanotubes through a filter membrane.
 3. Themethod of claim 2, wherein the filter membrane has a first electrostaticfield during the filtering the individual nanotubes.
 4. The method ofclaim 3, wherein the individual nanotubes are surrounded by a spacermaterial during the filtering the individual nanotubes, the spacermaterial having a second electrostatic field.
 5. The method of claim 4,wherein the stack of nanotubes has a nanotube density of about 500nanotubes per micrometer.
 6. The method of claim 4, wherein the spacermaterial comprises a surfactant.
 7. The method of claim 1, furthercomprising, after the removing the supporting layer, removing a spacermaterial from around at least one nanotube within the remaining portionof the stack of nanotubes.
 8. A method of manufacturing a semiconductordevice, the method comprising: filtering a carbon nanotube solutionthrough a filter membrane, the filter membrane having a electrostaticfield, wherein during the filtering a first layer of carbon nanotubes, asecond layer of carbon nanotubes, and a third layer of carbon nanotubesare deposited on the filter membrane; transferring the first layer ofcarbon nanotubes, the second layer of carbon nanotubes, and the thirdlayer of carbon nanotubes to a dielectric layer over a substrate;removing the third layer of carbon nanotubes with a destructive removalprocess; removing the second layer of carbon nanotubes with anon-destructive removal process; and forming a gate electrode over thefirst layer of carbon nanotubes after the removing the second layer ofcarbon nanotubes.
 9. The method of claim 8, wherein the destructiveremoval process comprises a reactive ion etching process.
 10. The methodof claim 9, wherein the non-destructive removal process comprises amechanical exfoliation process.
 11. The method of claim 10, wherein themechanical exfoliation process further comprising depositing asupporting layer over the second layer of carbon nanotubes, and whereinthe mechanical exfoliation process removes both the supporting layer andthe second layer of carbon nanotubes.
 12. The method of claim 11,wherein the mechanical exfoliation process further removes carbonnanotubes damaged during the destructive removal process.
 13. The methodof claim 8, further comprising removing a spacer material from carbonnanotubes within the first layer of carbon nanotubes.
 14. The method ofclaim 13, wherein the first layer of carbon nanotubes has a density ofabout 500 nanotubes per micrometers.
 15. A method of manufacturing asemiconductor device, the method comprising: receiving a solution, thesolution comprising carbon nanotubes; aligning the carbon nanotubesusing a first electrostatic field into a stack of aligned carbonnanotubes; placing the stack of aligned carbon nanotubes onto adielectric material; thinning the stack of aligned carbon nanotubes afirst time with a first process; thinning the stack of aligned carbonnanotubes a second time with a second process different from the firstprocess; and depositing a source/drain contact in electrical connectionwith the stack of aligned carbon nanotubes after the thinning the stackof aligned carbon nanotubes the second time.
 16. The method of claim 15,wherein the first process is an etching process.
 17. The method of claim16, wherein the second process is an exfoliation process.
 18. The methodof claim 15, wherein the first electrostatic field is generated by amaterial located on a filter membrane.
 19. The method of claim 18,wherein the carbon nanotubes are surrounded by a spacer material duringthe aligning the carbon nanotubes, the spacer material generating asecond electrostatic field.
 20. The method of claim 15, wherein afterthe thinning the stack of aligned carbon nanotubes the second time athickness of the stack of aligned carbon nanotubes is less than 2 nm.